Apparatus for subsurface exploration



p i 1954 J. JAMES, JR

APPARATUS FOR SUBSURFACE EXPLORATION 2 Sheets-Sheet l -m m l m Ema-EFF .H

Filed Nov. 16, 194a April 1954 V 1. .1. JAMES, JR 9 APPARATUS FOR SUBSURFACE EXPLORATION Filed NOV. 16, 1948 2 Sheets-Sheet 2 [on/5,? 97 95 If; #667,?

(I I I ...w .EZG': .72- Eli-1J3.

ar M

Patented Apr. 6, 1954 UNITED STATES PATENT OFFICE APPARATUS FOR" SUBSURFACE EXPLORATION Ivor J. James, Jr., Bellflower, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of" California Application November 16, 1948', Serial No. 60,244

4 Claims. 1

pressures and temperatures and the like.

The determination of such data is especially important with respect to boreholes drilled into subsurface strata to effect recovery of valuable fluids therefrom. In some cases it is desired to deliberately drill a slanting well which deviates in a known manner from the vertical in order to supply or withdraw fluids to or from a given position in a known formation. In offshore drilling, accumulations of valuable fluids such as crude oil or others situated in strata beneath the ocean floor may be produced therefrom by deliberately drilling an inclined borehole from a shore line position. In these instances it is highly desirable to know to a significant degree of accuracy the actual inclination of the borehole so that drilling may be conducted in such a manner as to complete the well into the desired strata.

It is therefore an object of the present invention to provide an improved apparatus for determining pertinent physical data from subsurface openings.

It is a further object of this invention to provide an apparatus especially adapted to the determination of physical data from well bores drilled into the subsurface.

Another object of this invention is to provide an accurate means for the measurement of pressures, temperatures, and depths of subsurface well bores as well as their inclination from the vertical.

A more specific object of this invention is toprovide an apparatus consisting of at least one.

variable frequency electrical oscillator, the frequency of which is altered in a known manner with the inclination of the borehole, means for transmitting this variable frequency from the well bore to the surface, and means for taking desired physical data from the variable electrical oscillation received at the surface.

Other objectsand advantages of this invention will become apparent to those skilled in the art as the description thereof proceeds.

Briefly, the present invention comprises a method for determining subsurface pressures, temperatures, depths and inclinations from subsurface openings such as well bores by means of an electrical oscillator, the frequency of which is variable in accordance with at least one of the aforementioned properties of the subsurface opening. In the preferred modification of this invention the subsurface property which it is desired to determine is allowed to influence the frequency of an electrical oscillator such as one which generates electrical oscillations in the radio-frequency range. By suitably connecting the electrical oscillator or oscillators to a transmission line, the variable electrical oscillation thus produced is received and detected at the surface whereby the physical property affecting th oscillator frequency may be determined.

Specifically this invention comprises the employment of at least one variable frequency oscillator preferably generating electrical oscillations having a frequency in the radio-frequency range which extends from about 15,000 cycles per second to as high as 5,000 megacycles and higher,

which oscillator is provided with a frequency determining circuit comprising an electrical inductance and an electrical capacitance. This inductance and capacitance may be connected in parallel or in series depending upon the particular modification of oscillator in which these circuit components control the oscillation frequency. The physical properties such as pressure, depth, temperature or inclination are caused to act upon this frequency determining circuit to alter the oscillation frequency in a particular manner so that the magnitude of the physical property may be determined by measuring the oscillation frequency itself or a change in the oscillation frequency.

The magnitude of the variable frequency oscillation is increased by using suitable amplifiers such as those of the vacuum tube type so that an oscillation of sufficient magnitude is obtained to permit transmitting the oscillations from the oscillator in the subsurface to a detection means in which the frequency is determined. In general it is preferable to suspend the oscillator in the subsurface in the region where the physical property desired is manifest. It is also preferable to position the detection means at the earths surface where the variable frequency is measured ductance may be physically arranged to be affected by changing pressures to suitably alter the oscillation frequency in accordance therewith. To measure subsurface depths, the hydrostatic pressure exerted by a given fluid present in the subsurface opening is determined by the variable frequency oscillator and the depth may be determined by suitable direct reading instruments or by calculation. To determine subsurface temperatures, the preferred embodiment of the present invention comprises the employment of an electrical capacitance having a known capacitance-temperature relationship in conjunction with the frequency determining circuit mentioned above whereby direct exposure of the capacitance to the temperature conditions within the subsurface opening will cause the capacitance and simultaneously the frequency to vary in a known manner. To determine the inclination of the borehole from the vertica1 it is preferred in this invention to employ at least two variable frequency oscillators, the frequency of which changes with the inclination from a vertical position. The preferred embodiment of apparatus for measuring such inclination incorporates a pair of variable radio-frequency oscillators the frequency of which is altered by changes in capacitance of the frequency determining circuits. Preferably the capacitance is varied by the motion of at least one pendulum or other gravity sensitive member which may be employed as one electrode of the capacitances. By employing frequency determining circuits which vary in accordance with incl nations and in different planes of known relationsh p to each other, the determination of the individual frequencies of the oscillators or in some cases the determination of the frequency difference as well as the frequency serves to accurately determine the inclination with respect to the vert cal or any other reference line. In the preferred embodiment of this invention a gyroscope control of portions of the frequency determining circuit is maintained in order that the relationship between the inclination of the subsurface opening and a given azimuth direction may be known. In one modification the gyroscope control is employed to maintain one of the variable capacitances mentioned above operating in a plane passing through a horizontal north-south line so that the radiofrequency oscillator associated with the part cular variable capacitance continuously indicates the inclination in the north-south'plane. ond oscillator, the variable capacitance or inductance of which is gyroscopically mainta ned to be actuated by physical movements acting in a second plane of known relationshi to the northsouth plane, permits the precise determination of inclination and azimuth readily through measurement of the frequency of the two electrical oscillators. In another embodment of this invention gyroscopic control of a third oscillator may be obtained so that separate indications of azimuth and inclination may be obtained.

Such a third oscillator may comprise an electrical oscillator generating oscillations having frequencies in the audio-frequency range extending from about ten cycles per second to more than 10,000 cycles per second. l his variable audiooscillation may be employed to modulate one of the aforementioned electrical oscillators operating in the radio-frequency range to identfy that particular oscillator as well as to convey an indication of the azimuth from the exploration in- A secstrument to the detection means which may be positioned at the surface.

The methods and apparatus of the present invention may be more clearly understood by reference to the accompanying drawings in which:

Figure l shows'a schematic cross section of the exploration instrument adapted to the determination of inclination and azimuth of subsurface openings such as' a borehole,

Figure 2 shows a horizontal plan view of one disposition of the elements of the variable capacitance employed in one embodiment of the frequency determining circuits employed in the radio-frequency oscillator,

Figure 3 presents a simplified circuit diagram of a variable frequency oscillator adapted to the generation of electrical oscillations in the radiofrequency range,

Figure 4 shows an'elevation view of a pair of plate type variable capacitances actuated by pendulums moving in planes disposed at a known angle to each other,

Figure 5 presents a simplified schematic d1agram of an electrical oscillator adapted to generating electrical oscillations having frequencies.

in the audio-frequency range and adapted tov modulate the output of one of the radio-frequency oscillators in accordance with the azimuth of the gyro control,

Figure 6 shows a schematic diagram of a circular variable resistance which may be associated with the gyro control to suitably vary the.

audio-modulation frequency in accordance with the azimuth when this type of azimuth determi-v Figure 11 shows a vertical cross section of part' of the frequency determining circuit in which a permeability tuned variable inductance is used' to vary the oscillator frequency inaccordance. ,with subsurface pressures,

Figure 12 shows a vertical cross section of the apparatus of Figure 11 wherein the inductance is directly varied by changing its dimensions,

Figure 13 shows the apparatus of Figure 11 wherein a variable capacitor causes frequency changes in accordance with the subsurface pressure.

7 Figure 14 shows a vertical cross section of the. frequency determining apparatus wherein sub-' surface temperatures are measured.

Figure 15 shows a vertical cross section of the exploration instrument in which a pair of circular resistances shown in Figures 5 and 6 and.

actuated by pendulums are used to indicate inclination,

Figure 16 shows a plan view of the pendulum, circular resistance, and connecting gears,

Figure 17 represents a schematic diagram of the oscilloscope pattern obtainable from the apparatuses described in conjunction with Figure and "Figure 18 indicates diagrammatically a conventional wave or frequency meter for measurement of the frequency of electrical oscillations.

Referring now more particularly to Figure 1, an elevation view in cross section of one modiflcation of apparatus for measuring inclination is shown. The constituent parts of the exploration instrument are contained in housing I which is suspended in the subsurface by means of suspension cable I I which also functions as a conductor of the electrical oscillations to the surface. Housings III contains a pair of electrical transmission oscillators I2 and I3, a modulation oscillator I4 connected to modulate the output signal of radio-frequency oscillator I3 and thereby identify it from the output signal of radio-frequency oscillator I2, chamber [5' containing gravity sensitive member it such as a pendulum in proximity to stationary mem-- bers I1 and I8 which are insulated from housing III, chamber I9 containing a gyroscopically actuated member 20 provided with bearings 2I and 22 permitting member 20 to rotate freely about the longitudinal axis of housing I0 while indicating azimuth, and power supply chamber 23 con-v taining sources of power for operating electrical constituents of the apparatus. Housing I 0 is elongated and preferably of cylindrical shape having a diameter which permits it to be lowered and raised freely through a subsurface opening such as a borehole. The length of housing I0 need be only suflicient to provide volume required for constituent parts of the apparatus named above. Chamber I5 may be at least partially filled with a damping fluid to substantially eliminate the natural periodic oscillations of gravity sensitive member I6. Transformer oils are especially well suited to this purpose where high dielectric constant and the proper viscosity at the temperature of the subsurface may be obtained to limit the periodic motion.

Stationary members I I and I3 each are connected as part of the frequency determining circuits of transmission oscillators I2 and I3 since an electrical capacitance exists between each of members I1 and I8 and gravity sensitive member I6. Thus, when the longitudinal axis of housing l0 departs from the vertical to align itself with an inclining borehole, or the like, gravity sensitive m mber IE remains aligned with the vertical. The resultant movement of gravity sensitive member I6 with respect to stationary members I! and IB causes a changein electrical capacitance which is in proportion to the inclination of housing It. The frequency of at least one of electrical oscillators I2 and I3 changes proportionally with the inclination to a higher or lower value.

A plan view of a cross section of the chamber containing gravity s nsitive member [6 centrally situated with respect to stationary members I! and I8 is shown in Figure 2. Connections 26, 21, and 2B are the same as those indicated in Figure- 1. The angular spacing 0 between stationary members I I and I8 may be between as low as to as high as 180, but preferably this spacing is between about 60 and 150. spacings of 90 or 120 are representative ones which permit accurate inclination measurements.

Within chamber I 5 shown in Figure 1, stationary members I1 and I8 are electrically insulated from housing I0 by means of insulators 24 and 25 while being electrically connected by means of connections 26 and 2.1 to the frequency determining circuits of transmission oscillators 12' 6. and I3, respectively. Gravity sensitive member I6 is also connected to the frequency determining circuits by means of connection 28 so that proportional frequency variations may be made in the transmission oscillators I2 and I3 from motion of gravity sensitive member IS with respect to stationary members 11 and I8 as described above.

In Figure 3 is shown a simplified schematic wiring diagram of a transmission oscillator in. which the variable frequency output required may be obtained. Such an oscillator is of the vacuum tube type and provided with vacuum tube 39; a frequency determining circuit consisting of paralleled inductance 40 and capacitance 4I connected between ground 42 and. control grid 43. The frequency of oscillation is determined by the values of inductance and capaci-, tance in this circuit according to in which 1 is the resonant frequency in megacycles, L the inductance in microhenries, and C the capacity in micromicrofarads.

Part of the capacitance of the circuit is included between stationary member 44 tapped onto inductance and corresponding to either member I! or I8 of Figure 1 and gravity sensitive member I 6. Changes in the relative position of gravity sensitive member IS with respect to stationary member 44 of Figure 2 changes proportionally the capacity of the frequency determining circuit causing a frequency change predictable from the equation given above.

Power is supplied to filament 45 provided by battery 46, screen grid voltage by battery 41, and plate voltage by batteries 4! and 4B in series. Switch 42a serves to disconnect power from filament 45 and the plate circuit. The electrical oscillations are amplified so that electrical current and voltage variations are obtained from the oscillator in the output circuit. The output circuit includes plate or anode 49, coupling capacitance corresponding to either capacitance 3| or 32 in Figure 1, radio-frequency choke SI, and connections of these elements to each other and the power sources. It also includes connections 52 and 53 with shorting bar 54 for introducing an audio-frequency modulation to identify the signal obtained.

Referring now again to Figure 1, energy of variable frequency'is conducted from transmission oscillators I2 and I3 by means of connections 29 and 30 containing coupling capacitances 3| and 32 respectively to connection 33. Energy is conducted therefrom by means of suspension line I I to the surface where the inclination of the exploration instrument is determined from frequeney or frequency change measurements with frequency measurement apparatus well known in the art such as accurately calibrated radio receivers, heterodyne frequency meters and the like as indicated generally in Figure 13. Conventional radio-frequency amplifiers may be added to the oscillator to increase the amplitude of the variable frequency signal obtained if desired.

Changes in capacity for frequency variation may also be obtained using the conventional plate-type variable capacitances shown in Figure 4. In this modification, the two condensers 55 and 55 are oriented at an angle to each other and are actuated by gravity sensitive members 51 and 58, respectively. Each may be connected to the frequency determining circuit of an elecfrequency of the transmission oscillators.

trical oscillator as described above, and the frequency changes resulting correlated with inclination. Conveniently the axes of capacitor rotors 59 and 60 are at an angle of about 90 to each other, although other angles may be used. Since two transmission oscillators are employed', as shown in Figure l, and so they may be conveniently operated at approximately the same frequency, a means is provided to difierentiate the signal of oscillator I3 from that of oscillator l2. This is accomplished by providing modulation oscillator M which modulates the signal from oscillator l3 at an audio-frequency for example. The modulation oscillator in this modification has another function if desired, or a separate means may be provided, for continuously indicating the orientation of the exploration instrument with respect to a given geographic direction. so that the indication of inclination given by the transmission oscillators frequency variation may be interpreted properly. In one modification of the invention, the frequency of the audio-modulation may be varied. in accordance with the azimuth indicated by gyro member 20 which may be preset at the sur-. faces In Figure 5, a schematic wiring diagram of a modulation oscillator is shown which is capable of difl'erentiating the signals of the two transmission oscillators as well as indicating the geographic orientation of the exploration instrument inthe subsurface. of the vacuum tube type and generates a variable audio-frequency signal to modulate the signal generated by either one of the transmission oscillators. The frequency of the oscillation is dependent largely upon the frequency determining circuit comprising inductance El capaci-' tance 62 and resistance 63. This circuit is connected to vacuum tube 64 which amplifies the oscillation. The output circuit comprising plate or anode 65, output transformer 66, plate power supply battery 6?, and electrical connections joining these components with each other delivers energy in the form of an electrical oscillation at an audio-frequency to output terminals 68 and B9. The shorting bar 54 shown in Figure 3 is removed from terminals 52 and 53 which are connected to terminals 68 and 69, respectively, shown in Figure 5. In the latter figure, output transformer 66 is provided with a parallel variable resistance 10 which permits a controlled amount of 7 energy at an audio-frequency to be. introduced into the signal of one of the transmission oscillators... The presence of this audio-modulation is readily detectable on the transmission oscillator signal in a suitable receiver and one signal thereforemay be differentiated from the other.

.A constant frequency of audio-modulation is all that is needed for signal differentiation, however, a means for indicating orientation of the exploration instrument in the subsurface with respect to a geographic direction is necessary for proper interpretation of the borehole inclination data obtained from measurement of the variable This azimuth data may be transmitted from the exploration instrument in the form of a variable audio frequency modulation of the signal from one of the transmission oscillators. In Figure 5 resistance 63 is shown connected in series with the frequency determining circuit and it has the effect of lowering the oscillation frequency as the resistance is increased. For the oscillator shown where;;lndustance 6| base value of about 1.2

The modulation oscillator is 8 henries, capacitance 62 a value of about-0.150 microfarad, and resistance 53 is variable from zero to about 5,000 ohms, the audio-frequency.

range will be from about to about 400 cycles per second. Referring again to Figure 1, gyro member 20 is provided with rotor 34 and power supply 35. If desired, power may be applied through a com-'- mutator. from power supply chamber 23. ings 2| and 22 permit gyro member 20 to maintain a given preset azimuth while housing Ill of the exploration instrument may turn about its longitudinal axis. with sliding contact 36 which rests on the resistive element of circular electrical resistor housing in by attachment to lateral divider 38.

This resistor is resistance 63 shown in Figure 5: As rotative motion occurs between gyro member" 20 and housing 10, sliding contact 36 joins circular resistor 31 in a different position. A

change in the electrical resistance of resistor 31'- inclucled between the point of sliding contact" The electrical connection of sliding contact 36 with the modulationoscillator may be made through bearing 21 or" 36 and one terminal results.

through a commutator not shown. This change in resistance with rotary motion of the explora-f tion instrument serves to vary the frequency of the modulation oscillator proportionally as described above.

inclination of the borehole from the vertical as well as the azimuth of the incline. I With gyroscopic control of the azimuth deter mination, gyro member 20 of Figure 1 may be preset at the surface prior to subsurface explora tion with the instrument to a known magnetic to vary the frequency of audio-modulation as described above.

In Figure '7 is shown a modification of the apparatus of this invention in which gyroscopic member it maintains stationary members l5 and 16 in a fixed geographic orientation while any rotation of the exploration instrument housing during passage through a borehole may occur.

Such rotation in this modification has no effect on the inclination determinations. Stationary members 15 and 16 are made part of the fre-' quency determining circuits of two transmission oscillators such as described in connection with Figure 3. Gravity sensitive member I? is conimon to both frequency determining circuits and the inclination is detected in the manner described above. A modulation oscillator is not. strictly necessary if the transmission oscillators have sufficiently different frequency ranges that these do not overlap during operation. Should both oscillators have the same frequency when the instrument is in a vertical position, then the modulation oscillator is provided to differ entiate one signal from the other.

In Figure '7, gyro member 14 is supported on bearings 18 and 19 and contains rotor 80. 'P'ower? Bear Gyro member 20 is provided 31- which is integrally attached to and rotates with Detection of the frequencies ofthe two transmission oscillators and that of themodulation oscillator accurately determines the to actuate the rotor as well as connections for members 15 and 16 are preferably brought through commutator Power for rotor operation may be brought through contacts 82 and B! at bearings I8 and I9, respectively.

A plan view of the apparatus of Figure 7 is shown in Figure 8 in which gyro member 80 is shown with stationary members 15 and I6 arranged at an angle 0 of 90 to each other adjacent to gravity sensitive member II. The gyro may be preset to align stationary member I in a north-south plane and member "It in an eastwest plane. Frequency change determinations are therefore readily convertible into inclination vectors 84 and 85 giving vector 86 shown in Figure 9. This vector shows the degree of in clination by its length and the azimuth. In this instance where one of the stationary members is disposed in a north-south plane, angle a shown in Figure 9 is zero. In any modification, angle a is known and preset prior to introduction of the instrument into the hole and angle 01 or H2 is the angle between the stationary members as described above.

Where gyro control of the stationary members is not employed, the frequency change of one transmission oscillator having a stationary member at point 01 in Figure 9 determines the position of the gravity sensitive member along an are 88 or another are having the same center. The frequency change of the second oscillator having a stationary member at point 89 spaced 02 degrees from point 81 determines the position of the gravity sensitive member as on an are 90 or one having its center at point 09. The intersectionof these arcs locates point 9|. A vector 92 drawn from point 93, the center correspondin'g'to the-vertical position of gravity sensitive member, to point 9I shows the degree of inclination by its length and the direction by its angle wlth'respect to other means such as the audiomodulation oscillator frequency variation or a gyro'member determines angle a and the inclination and .direction is completely determined.

In Figure 10 is shown an illustration of the changes in transmission oscillator frequency with inclination in various directions. In this diagram It) represents the frequency of these oscillators in the vertical position; When the instrumentisinclined in a direction to move the gravity sensitive member away from both stationary members, decreasing the capacitances, the frequencies risetovalues depicted by in for the nonmodula'ted oscillator and fm for the modulewd-oscillator. The frequency change vectors 95 and Git-correspond to vectors of motion of the gravity sensitivemember. The motion vectors determine the magnitude and direction of the movement-of the gravity sensitive member and determine the magnitude and azimuth of the inclination. Frequency changes to values lower than ,0 indicate that the capacity between the particular stationary member corresponding to that signal -and the gravity sensitive member is increased by movement to decrease the distance between" the-two-membe'rs. Vector '91 gives a measure-oi the inclination giving this movement. I The method and apparatus of this inventionwhlch' involves the variation 'of-frequency generated'by an electrical oscil-lator maybe applied to the obtaining of other desirable physical data from thesubsurtace. According to-the methods described hereinafter --subsurfaoe temperatures, pressures anddepths may be determined.

aterring nowto Figure 11 a cross-sectional view of housing 98 is shown provided in the lower portion thereof with openings 99 by means of which the subsurface pressure is applied directly to portions of apparatus within housing 98. Chamber I00 is provided between dividers HM and I02 and inductance W3 is suspended therein. Conductors I04 and I05 connect inductance I03 to other portions of the frequency determining circuit in an electrical oscillator described above but not shown in this figure. Bellows I06 attached to divider I02 is exposed on the under side to the subsurface pressure and on the upper side is connected directly to metallic slug I0I by means of rod I68. Changes in subsurface pressure cause bellows I08 to expand and contract thereby moving slug I07 to different positions within inductance I03. Such a variable inductance is known as a permeability tuned inductance and the frequency of the. electrical oscillator is thereby varied in accordance with the subsurface pressure. If metallic slug IN is fabricated from a ferrous alloy such as iron, steel, an iron nickel alloy or the like, the resonant fre quency of the oscillator decreases as the slug is moved into the coil; whereas copper or copper alloy slugs cause the resonant frequency to increase as the slug is moved into the coil. Either type of slug may be employed with equal success and a choice will depend largely upon particular circumstances.

In Figure 12 another modification of the apparatus just described is shown in which changes in frequency of the electrical oscillator with subsurface pressure are effected by changing the actual physical dimensions of the inductance in the manner of a spring. Inductance IE3 is caused to expand and contract as bellows I08 moves under the influence of external pressure applied to the inner portion thereof via holes 99 in housing 98. Inductance I03 is connected to the frequency determining circuit of an electrical oscillator whereby changes in subsurface pressure acting indirectly on inductance I03 cause the frequency of the oscillator to vary. Increases in pressure in this particular modification causing inductance to increase while decreases in pressure cause the inductance to decrease while the frequency of the oscillator decreases and increases, respectively. The same parts of apparatus shown in Figure 12, 13 and 14 are numbered identically with those in Figure 11.

Referring now to Figure 13 a modification of apparatus is shown in which subsurface pressure changes indirectly actuate a capacitor connected to the frequency determining circuit of an electrical oscillator. Housing is provided with divisions I01 and I02, in the lower of which bellows I06 is attached. A capacitor having stationary electrode I05 and movable electrode H0 is provided, the latter electrode being directly attached by means of rod I08 to bellows I05. Connections I04 and I05 connect the variable capacitor directly to the frequency determining circuit of an electrical oscillator whereby frequency variations in accordance withsubsurfa-eepressures are obtained. The particular advan,- tage of this modification resides in the greater frequency change per unit degree of expansion of bellows I00 at high pressures wherein the 'bel-z lows I-IIE-iseXtended. A particular type of bels lows may be employed therefor which is operable over a widerange' of pressures so that "small degrees of bellows extension in the higher pres sure -rangesyield readable -frequency changes;

Themethod and apparatus of the-present hit-- vention may be applied to the measurement of subsurface temperatures as is shown in Figure 14. Housing 98 is provided with openings 99, divider I02, and with additional opening III through which fluid may enter to leave via openings- 99. The frequency determining circuit of an electrical oscillator is positioned in chamber II2 above divider I02 and contains inductance H3 provided with connections H4, H5 and H6. A capacitance H1 is connected in parallel with inductance I3 and is preferably a capacitor hav ing a zero temperature-capacitance coeiiicient so that the frequency determining circuit present in chamber H2 is unaffected by temperature. Another capacitor H8 is positioned directly in line with opening I I I and is connected by means of connectors I I9 and I in parallel with capacitor H1. Capacitor H8 is that type having a positive or negative temperature-capacitance coefficient so that as the temperature is varied the capacitance and the frequency of the electrical oscillator change. In the case of where capacitor H8 has a positive temperature coefficient, increases in temperature will bring about decreases in oscillator frequency. Where capacitor IIB has .a negative temperature coefficient, increases in oscillator frequency result from increases in temperature. It is preferable that the ratio of capacitance of capacitors H8 and Ill be such that changes in temperature directly acting upon capacitor H8 result in sufiicient frequency change that the desired degree of temperature determination is obtained. If desired, the entire capacitance of the frequency determining circuit may be lumped in capacitor H8 and capacitor III may be dispensed with. At least part of the capacitance in the circuit must have a temperature coefiicient difierent from zero.

The frequency determining circuits herein described in conjunction with Figures 11 through 14 correspond to the frequency determining circuit shown in Figure 3 which consists of inductance 40 and capacitor 4|. The electrical oscillator, also described herein as a transmission oscillator shown in Figure 3 is also applicable to the apparatus and methods described in Figures 11 through 14. These apparatuses are preferably operated in conjunction with apparatus to continuously determine or record the depth of the instrument from the surface. These apparatuses may also be operated either bymoving them continuously through a subsurface openingsuch as a well bore or by lowering them to different levels at which all motion is stopped while the pressure, depth, or temperature determination is made. In logging a borehole during the process of drilling or under other conditions where the borehole contains a fluid of known density, pressure measurements according to the methods described above may also be employed to measure depths.

The apparatus shown in Figures 11, 12 and 13 preferably are constructed using a frequency determining circuit having a zero temperature coeflicient so that pressure alone effects the fre- I quency of the transmission oscillator. If desired, separate oscillators may be employed according to the methods herein described to separately measure pressure and temperature in one logging operation.

.Reierring now particularly to Figure 15, avertical cross section of another modification of the exploration instrument according to this invention is shown in which the well bore inclination actuates a pair of gravity sensitive members which in turn actuate a, pair of circular resistors similar to the type described in Figures 5 and 6. Housing I 2| is provided with upper divider I22 and lower divider I23 forming chamber I24 in which the gravity sensitive members and their associated equipment are contained. If desired, chamber I24 may be filled with a liquid to dampen periodic oscillations of'the pendula as described above. A gyro member I25 provided with gyro housing I23 is supported by bearings I21 which may be circular ball or roller type bearings on supports I28 and I29. Power is supplied to the electrically driven gyro member I 25 via commutators I30 and I3I through connections I32 and I33. Structure I34 upon which circular resistors I35 and I36 are supported and insulated therefrom is indirectly attached to gyro housing I26 to rotate therewith relative to housing I2 I A plan view of such a circular resistor is shown in Figure 16 in which winding I3! is provided with contacts I33 andl39 and movable contact I40. In the present modification contact I40 is moved with respect to winding I3! by means of a pair of bevel gears HI and I42. Bevel gear I42 in turn is actuated by gravity sensitive member I43. By employing a pair of circular resistors with the associated contact, bevel gear, and gravity sensitive member equipment described and spacing them at an angle to one another as above described such as 90 an exact determination of inclination of the instrument with respect to a vertical line may be obtained. The two gravity sensitive members. I43 and I44 shown in Figure 15 are restricted to movement in one plane each at right angles to each other. Further, they are supported directly upon the gyro member by means of which a constant angle between said planes and a given geographic direction may be maintained. Therefore, by presenting the planes in which the gyro members may move to correspond with a northsouth and an east-west plane, the actual inclination as well as the azimuth may be obtained through direct or indirect readings of the circular resistances followed by a. vector summation of them. Connections to circular resistances I35 and I36 are made via commutator I45 provided with contacts I46 shown in Figure 15.

of resistor I31 between movable contact I40 and contact I38 be the same as the resistance between movable contact I40oand contact I39. That is,

movable contact I40 is electrically midWay::be.-'

tween the ends of circular resistor I31. Thus, as the gravity sensitive member I43 moves in plane I48 in response to changes in inclination, the

resistance between contact I41 and either of -con 'tacts I38 and I39 varies accordingly to provide a variable voltage or current from which the; degree of inclination in that plane may be directly determined from the constants of the;

. system by calculation or by previous calibration.

= As is indicated in Figure 15 a pair of circular.

resistances with gravity sensitive members toactuate them may be, positioned in planes at right angles to one another to obtain electrical indications of inclination, the vector sum of whiche directly indicate the azimuth and degree of infclination. The variable voltages thus obtained-, which may be either alternatingcurrent or direct; current voltages, may be employed to defiectthe i electronbeam ofthe, cathode ray oscilloscope by applying the voltage from one resistor to the horizontal deflection plates and the other voltage obtained to the vertical deflection plates, for

.whereby one gravity sensitive member moves in a northsouth plane and the voltage therefrom is applied to the vertical deflection plates of the tube. The other gravity sensitive member is permitted to move in an east-west plane and the voltage from the associated resistor is applied to the horizontal deflection plates of the tube.

A linear change in voltage may be obtained with inclination in each plane and a linear deflection of electron beam with which in deflection voltage may .be represented by vector I56 in the northsouth plane and by vector II in the east-west plane. Actually neither of these vectors are indicated on the cathode ray tube screen. However, point I52 is indicated as a bright spot denoting the point at which the deflected electron beam impinges on the screen and the vector summation is automatically made. A line drawn from screen center I53 to point I52 gives inclination vector I50 the length of which is the exact measure of the degree of inclination. The angle 6 included between inclination vector I54 and the north-south line is the azimuth of the inclination. In this manner a recordable representation of the azimuth and degree of inclination is obtained and it may easily be photographed in conjunction with a depth-reading device whereby a continuous photographic record of the azimuth and the inclination and the depth may be obtained. For such a photographic record a motion picture type camera is preferred, particularly where the exploration instrument is continuously moved through the borehole or other subsurface opening while the inclinations and depths are measured. Where the instrument is stopped at each level where an inclination determination is desired, an ordinary camera preferably modified to wind films automatically between exposures may be employed to photographically record the visual indications of the cathode ray screen and the reading on the depth indicator.

In another preferred modification of this embodiment of the invention the variable resistance above described in connection with Figures and 16 are applied to a pair of modulation oscillators operating in the audio-frequency range. The change in resistance causes the frequency of the audio-oscillation to change thereby indicating the inclination in a given plane. The audio-oscillator so employed may be one like that described in connection with Figure 5 and is employed to modulate a transmission oscillator similar to that described in connection with Figure 3. The transmission oscillator or oscillators in this case may be of the constant frequency type and the data from which the degree and azimuth of inclination is obtained is transmitted via an electrical conductor from the subsurface in the form of a variable frequency audio-modulation of the radio-frequency transmission oscillator.

In the description of the embodiments of the present invention variable frequency oscillators operating in the radio-frequency range have been described and it is intended that the radio frequency range so indicated be the same as the radio-frequency range well known to those in the art of radio communication, for example, from a lower frequency of about 15 kilocycles to high frequencies .of the order of 5,000 megacycles and higher. Preferably the operational range of radio-frequency is included between about 500 kilocycles and about 500 megacycles, although these specific ranges are not intended to limit the present invention. The audio-frequency range in which the variable frequency modulation 0s,- cillator operates preferably generates oscillation in the well known audio-frequency range between about 15 cycles and about 15,000 cycles per sec ond. However, modulation frequencies lower or higher than th limits given above may be used in conjunction with instruments capable of measuring such frequencies. In the case of the audio-frequency range, particularly those frequencies between about cycles per secondand 5,000 cycles per second, the measurement may be made with bridge typo instruments wherein an oscillation of known frequency is compared by ear to a beat frequency of zero whereby the unknown modulation frequency is determined.

A particular embodiment of the present invention has been hereinafter described in considerable detail by way of illustration. It should be understood that various other modifications and adaptations thereof may be made by those skilled in this particular art without departing from the spirit and scope of this invention as set forth quency determining circuit of both of said oscillators, a pair of separate stationary electrodes angularly disposed adjacent said gravity sensitive electrode forming a pair of variable capacitors, means connecting one each of said stationary electrodes to said frequency determining circuits of said radio-frequency oscillators, means for electrically transmitting radio-frequency oscillations from said housing to the surface, and means for measuring each of said radio frequencies to determine said deviation.

2. An exploration instrument for continuously logging the vertical deviation of a borehole drilled into the earth which comprises an elongated fiuid-tight housing, a suspension cable therefor, means for moving said housing through said borehole, a movable gravity sensitive electrode within said housing, two stationary electrodes angularly disposed adjacent said movable electrode and insulated therefrom forming a pair of variable capacitors having a common movable electrode, a radio-frequency electrical oscillator connected at'its frequency determining circuit to each of said stationary electrodes and to said movable electrode, an audio-frequency electrical oscillator of continuous and variable frequency output, power supply means for said oscillators, means for modulating the oscillation from one radio-frequency oscillator with the variable audio frequency oscillation from said audio-frequency oscillation, means for varying the frequency of said audio frequency oscillator in accordance with the orientation of said instrument with respect to a given geographic direction, means for electrically transmitting said oscillations through said borehole, and means to measure the frequency of said oscillations subi5 stantially at the earths surfac to determine the magnitude and the azimuth of said vertical deviation.

3. An apparatus for determining the inclination of bore holes which comprises an elongated fluid-tight housing provided with two transmismission oscillators and one modulation oscillator, said transmission oscillators having a frequency variable in the radio frequency range and said modulation oscillator having a frequency variable in the audio frequency range, a frequency deltermining circuit for each of said transmission oscillator comprising an inductance and a variable capacitor, a gravity sensitive movable electrode as a common electrode in each of said variable capacitors, a pair of stationary electrodes disposed in spaced relation to said gravity sensitive electrode forming said variable capacitors, a gyro member mounted within said housing, said stationary electrodes Supported by and insulated from said gyro member whereby said stationary electrodes are adapted to be maintained in a uniform orientation with respect to a given geographic direction, means connecting said modulation oscillator to one of said transmission oscillators and means for measuring the frequencies of said transmission oscillators and said modulation oscillator to determine the azimuth and the degree of inclination of said transmission oscillators comprising an inductance and a variable capacitor, a gravity sensitive movable electrode common to each of said capacitors, a pair of stationary electrodes in spaced relation to said gravity sensitive electrode forming said variable capacitors, a gyro member within said housing, a circular variable resistor adapted to be varied by the position of said gyro member in relation to said housing, said resistor being adapted to vary the audio frequency of said modulation oscillator continuously in accordance with the geographical orientation of said housing, power supply means for said gyro member, means connecting said modulation oscillator to one of said transmission oscillators and means for measuring the frequencies of said transmission oscillators and said modulation oscillator to determine the azimuth and the degree of inclination of said borehole.

, References Cited in the file of this patent UNITED STATES PATENTS- Number Name Date 1,928,969 Kufiel Oct. 3. 1933 1,928,970 Johnston Oct. 3, 1933 1,928,971 Dillon Oct. 3, 1933 1,988,458 Minorsky Jan. 22, 1935 1,999,215 Smith Apr. 30, 1935 2,018,080 Martienssen Oct. 22, 1935 2,116,120 Malmgren May 3, 1938 2,190,950 Potapenko Feb. 20, 1940 2,202,452 Hildebrand May 28, 1940 2,225,668 Subkow Dec. 24, 1940 2,262,245 Moseley Nov. 11, 1941 2,415,221 Savitz Feb. 4, 1947 2,425,868 Dillon Aug. 19, 1947 2,466,803 Giffen Apr. 12, 1949 2,507,351 Sherbatskay May 9, 1950 2,547,876 Krasnow Apr. 3, 1951 

